The present invention relates to an apparatus for supplying breathable gas to a human used in, for example, the Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea (OSA), other respiratory diseases/disorders such as emphysema or the application of assisted ventilation.
CPAP treatment of Obstructive Sleep Apnea (OSA) involves the delivery of a breathable gas (generally air) pressurised above atmospheric pressure to a patient""s airways via a conduit and a mask. CPAP pressures of 4 cm H2O to 22 cm H2O are typically used for treatment of OSA, depending on patient requirements. Treatment pressures for assisted ventilation can range of up to 32 cm H2O and beyond, again depending on patient requirements.
For either the treatment of OSA or the application of assisted ventilation or similar, the pressure of the gas delivered to patients can be constant level, bi-level (in synchronism with patient breathing) or auto setting in level. Throughout this specification reference to CPAP is intended to incorporate a reference to any one of, or combinations of, these forms of pressurised gas supply.
A disadvantage of existing CPAP gas supply apparatus, especially those used in hospitals and the like, is the danger of biological contamination and disease/virus/bacteria transfer. More particularly, there can be a significant reverse flow during heavy expiration and/or coughing and biological material exhaled by a patient can be deposited in the gas supply apparatus and transferred to another patient who uses the same machine. Further, a patient continually using the same machine can be re-infected by a prior condition.
Hitherto, CPAP apparatus have basically comprised a closed outer casing surrounding internal components. Components inside, and constituting part of, the gas flow path include the gas inlet, inlet filter, impeller, outlet muffler and gas outlet. Components outside the gas flow path include control electronics, power regulators and motor. As a result, present CPAP apparatus have a gas flow path that is extremely difficult to clean/sterilise without the time consuming dismantling and removal of all the xe2x80x9cgas flow pathxe2x80x9d components. Further, without disassembly, common sterilisation procedures such as autoclaving will damage the circuit boards and other electrical components.
An attempt to solve the above problem involves incorporating a bacteriological filter into the gas flow path adjacent the gas outlet to prevent biological material being forced back into the machine and any such material leaving the machine and being inhaled by the patient. However, these filters are expensive and add a significant resistance to the air path requiring larger and noisier fans and motors. A more restricted air path also represents a major difficulty to administering bi-level CPAP treatment due to the higher inspiratory air flow requirements of patients with advanced respiratory disease. Moreover, it is difficult to produce a biological filter which can trap very small biological particles such as viruses and spores that is still able to pass the required amount of air with an acceptable pressure drop, as decreasing filter pore size decreases hydraulic permeability.
It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above prior art deficiencies.
Accordingly, in a first aspect, the present invention provides an apparatus for supplying breathable gas, the apparatus including:
a main housing;
a sub-housing having a gas flow path between a gas inlet and a gas outlet;
a motive power source within the main housing;
an impeller within the sub-housing in fluid communication between the gas inlet and the gas outlet, the impeller adapted to releaseably engage the motive power source external the gas flow path,
wherein the sub-housing is releasably connectable to said main housing.
Preferably, the sub-housing includes one or more of an inlet filter, outlet muffler, gas flow rate sensing means, gas pressure sensing means or gas supply vent valve assembly.
Desirably, the motive power source is an electric motor.
Desirably also, the main housing includes one or more of a power supply and control system for the motor.
The motor preferably includes an output shaft terminating in an engaging formation adapted to releasably engage a complimentary engaging formation provided on the impeller.
The main housing preferably also includes a removable or pivotable lid adapted to restrain the sub-housing adjacent the main housing. In a preferred form, the lid includes acoustic shielding to reduce the emission of noise generated by the impeller and motor.
In a preferred embodiment, the gas flow rate sensing means includes a flexible flap in the gas flow path, the flap disposed between a light source and a linear image sensor respectively disposed either side of the flap and external to the gas flow path, whereby the amount of light incident on the image sensor is proportional to the deflection of the flap which is proportional to the gas flow rate.
In another preferred embodiment, the gas pressure sensing means includes a flexible membrane having one side in fluid communication with the gas flow path and an opposite side abutting a force probe coupled to a force transducer, whereby the displacement of the probe and transducer is proportional to the displacement of the membrane which is proportional to the gas pressure.
In yet another preferred embodiment, the gas vent valve assembly includes a gas venting conduit in fluid communication with the gas flow path, the gas venting conduit adapted to be selectively restricted by a cam abutting the gas venting conduit exterior, whereby varying the cam position varies gas passing through the gas venting conduit which varies the flow rate of remaining gas leaving the gas outlet.
Preferably, the motive power source includes a disk having magnets thereon and the impeller includes magnets mounted thereon, the disk magnets and the impeller magnets being adapted to attract.
Alternatively, the motive power source includes a disk having magnets thereon and the impeller includes a magnetically attractable plate mounted thereon, the disk magnets and the plate being adapted to attract.
In another embodiment, the motive power source includes a disk having magnets thereon and the impeller includes a non-ferrous metal plate, or a plate formed from a non magnetically attractable material having non-ferrous metal therein, mounted thereon.
In a further embodiment, the impeller includes a shaft having ferrite or other magnetic material mounted thereon and the main housing includes electric motor windings adapted to surround the ferrite or other magnetic material.
In a second aspect, the present invention discloses a method of cleaning, sterilising or disinfecting the gas flow path of the breathable gas supply apparatus of the first aspect, said method comprising the steps of:
(a) removing the sub-housing from the main housing, and
(b) cleaning, sterilising, disinfecting or replacing the sub-housing; and
(c) connecting the sub-housing to the main housing.